Now its working. Make sure both systems are on fixed local tcp/ip addresses, enable port forwarding on the gateway for ports 4000, 6112-6119 to the games host. Make sure both games are patched up, although you only need one CD. Join the game using the gateway’s internet address. I need to write a program to report this to the screen, currently I login into the gateway to get this.
Further notes and hints on my Diablo page on my wiki.